Diaphragm pumps

ABSTRACT

A diaphragm pump comprising a pumping chamber (10) is operated by a continuous flow of pressure gas to a driving chamber (12) separated from the pumping chamber by a flexible diaphragm (8 or 52). Deflection of the diaphragm by the gas pressure drives liquid out of the pumping chamber. The driving chamber has a normally closed outlet valve (30 or 54) connected to the diaphragm through a flexible or lost-motion connection (34, 36 or 56) so that the valve is opened after a certain deflection of the diaphragm. The driving chamber pressure is thereby released and allows the diaphragm to return, drawing further liquid into the pumping chamber. The return movement of the diaphragm also allows the valve to reclose and the cycle is repeated while the supply of pressure gas to the driving chamber is maintained.

BACKGROUND OF THE INVENTION

This invention relates to diaphragm pumps operated by gas pressure,particularly but not necessarily exclusively for medical services.

U.S. Pat. No. 4,319,570 discloses a fluid-pressure operated diaphragmpump to be used as an aspirator or tracheal suction pump. It has apumping chamber in part defined by a flexible diaphragm, the flexure ofwhich creates a suction in a drainage line. In a further chamberseparated from the pumping chamber by a secondary sealing diaphragm is avalve mechanism comprising inlet and outlet valve members which areopened and closed in opposition to each other as the diaphragmreciprocates, the opening of the outlet valve being triggered by theflexure of the diaphragm to a position of maximum pumping chamber volumeand the opening of the inlet valve being triggered by a return springthat is operative when the diaphragm flexes to a position of minimumpumping chamber volume. The valve mechanisms required in this pump arerelatively complex. They therefore carry an increased risk ofmalfunction in addition to being relatively expensive to produce. Costis particularly important if the valve is to be disposable, as is oftenrequired for surgical apparatus.

Another pressure-fluid operated diaphragm pump is disclosed in U.S. Pat.No. 4,662,829 in which pumping and driving chambers are separated by aflexible diaphragm and the driving chamber is connected continuously toa pressure air source. The flexible diaphragm is stretched over anexhaust port of the driving chamber during the contraction of thepumping chamber, by virtue of the pressure differential between thepumping chamber and the exhaust line, until the continuing flexure ofthe diaphragm under the driving fluid pressure forces the port open. Atthat stage, the pressure in the driving chamber is released via theexhaust port, the diaphragm collapses onto that port, and the cyclebegins again.

Although this pump has a relatively simple mechanism as compared withthe previously described example, it has inherent disadvantages. Inparticular, in order for the diaphragm to maintain a seal with thedriving chamber exhaust, a portion of its area must be held stationaryduring the pumping stroke despite the fact that the deflection of thediaphragm that is lost thereby reduces the pumping rate. It is possibleto compensate for this to a limited extent by employing more flexiblediaphragm materials but the risk of overstressing and rupture of thediaphragm is then increased, and such measures cannot make up for thelimitation of the pumping rate for any given size of pump due to thefact that part of the diaphragm is not participating in the pumpingstroke.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a fluid-pressureoperated pump comprising a pumping chamber having inlet and outletopenings for a fluid to be pumped and a fluid pressure driving chamber,a flexible diaphragm between the pumping and driving chambers beingdisplaceable by the driving fluid pressure to pump fluid through thepumping chamber, said driving chamber having an inlet for a pressurefluid supply for reciprocating the diaphragm and an outlet valve biasedto a closed position, means connecting the outlet valve to the diaphragmand permitting limited deflection of the diaphragm by the pressure ofthe fluid in the driving chamber without displacement of the valve fromsaid closed position, diaphragm displacement by the pressure fluidbeyond said limited deflection acting through said connecting means toopen the outlet valve and reduce the driving chamber pressure therebyreversing the direction of displacement of the diaphragm to permit thevalve to return to the closed position and allow the pressure in thedriving chamber to increase again.

In one form of the invention, the outlet valve comprises or is securedto a member that is flexibly deformable to release pressure from thedriving chamber. In another form of the invention, a flexibly deformablemember is arranged to release pressure from the driving chamber when inan undeformed state and, by its deformation, to allow the limiteddisplacement of the diaphragm while the outlet remains closed.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will be described in more detail, by way ofillustration of the invention, with reference to the accompanyingschematic drawings, in which:

FIG. 1 is an axial cross-section of one form of pump according to theinvention,

FIG. 2 shows a modification of the pump in FIG. 1, and

FIG. 3 shows another form of pump according to the invention in axialcross-section.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, the pump has a three-part casingcomprising a central generally cylindrical part 2 and top and bottomcovers 4, 6. Between the central casing part and the bottom cover, aflexible diaphragm 8 is clamped at its periphery. The diaphragm forms afluid-tight boundary dividing the casing interior into a lower liquidpumping chamber 10 and an upper pressure-gas driving chamber.

The casing bottom cover 6 has an inlet 16 and an outlet 18 for thepumping chamber 10. The inlet 16 is provided with a non-return valve 20in the form of a flexible moulding with sealing lips that open only toallow a flow into the chamber.

The main casing part 2 has a restricted inlet 22 opening into thedriving chamber 12 for connection to a source of pressure gas, eg. air.The top cover 4 has a central outlet port 24 from the driving chamber,and an outlet valve seat 26 surrounds that port.

On an inner peripheral shoulder in the central casing part 2, thererests a valve disc 30, shown in its sealing position in which it bearsagainst the valve seat 26. The disc 30 is a bistable plate that can besnapped over from the upwardly convex form illustrated to a downwardlyconvex form in which it is spaced from the valve seat. Independently ofthe position of the disc, there is free communication between the casingspaces above and below it through reliefs 32 in the shoulder.

Connecting the diaphragm 8 and the valve disc 80 is a lost motionmechanism comprising upper and lower links 34,36 anchored to the centresof the disc 30 and the diaphragm 8 respectively. The two links haveinterconnecting ends in the form of a hook 34a and a ring 36a whicheffectively operate as a pin and slot connection. Each link is thus ableto move axially to a limited extent relative to the other, as determinedby the internal height of the ring 36a and the vertical thickness of thearm of the hook 34a passing through the ring.

In use, pressure air is supplied continuously to the inlet 22. Thediaphragm 8 is deflected downwards from the position shown by thepressure in the driving chamber to expel liquid from the pumping chamberoutlet 18. As the diaphragm deflects, its link 36 descends until the topsection of the ring 36a engages the hook 34a. The valve disc 30 is thenpulled down until it snaps over to its downwardly convex state, openingthe driving chamber 12 to the outlet port 24. With the outlet 24 open,the restricted inlet 22 is unable to maintain pressure in the drivingchamber 12, so that the diaphragm rebounds to its undeflected state,increasing the volume of the pumping chamber 10 to draw more liquid inthrough the non-return valve 20. As the link 36 rises with the diaphragm8 to strike the top section of the hook 34a the valve disc 30 is snappedback to the upwardly convex position in which it is shown. The drivingchamber outlet 24 is once more sealed off and the cycle begins again.

The action of the pump can be stopped simply by the use of a shut-offvalve (not shown) in the pumped liquid outlet line from the outlet 18.While pressure continues to be applied to the driving chamber inlet 22,the pump restarts automatically when that outlet valve is opened.

In FIG. 2, the reference numbers of FIG. 1 are used for the same parts.The pump is, however, modified by replacing the bistable valve disc 30with a rigid valve body 40 biased by a spring 42 to the closingposition. The valve body 40 is fixed to the hooked link 34 and it has aresilient sealing layer 44 that bears against a valve seat 46 formedintegrally in the top cover 4 around the outlet port 24. The modifiedpump operates in an identical manner to the pump of FIG. 1 except thatthe driving chamber valve body 40 is continuously biased to its upwardposition by the spring 42 which can thus accelerate the return movementof the diaphragm between pumping strokes.

In FIG. 3, parts similar to those already described are again indicatedby the same reference numbers. In this embodiment the pump has aone-piece moulding 50 providing diaphragm 52, valve plate 54 and aninterconnecting flexible stem 56. The stem may be straight in itsrelaxed state but is able to act as a collapsible strut when placed incompression. A resilient spider 58 has a central recess housing thevalve plate 54. Radial legs 60 on the spider bear flexibly on aperipheral shoulder 62 inside the driving chamber 12 to urge the valveplate 54 against the seat 46 surrounding the driving chamber outlet 24.

In operation, during the pumping stroke the downward flexure of thediaphragm 52 by the pressure applied in the driving chamber first allowsthe stem 56 to straighten and then pulls the valve plate 54 off the seat46 to release the pressure in the driving chamber. As in the previousexamples, the pressure drop in the driving chamber allows the diaphragm52 to rise upwards, so that first the driving chamber outlet 24 isreclosed and then the compression load on the stem 56 causes it tobuckles elastically. The mechanism thus returns to its illustrated stateand the cycle is repeated while pressure gas continues to be supplied tothe driving chamber and the outlet from the pumping chamber remainsopen.

It is of course possible to substitute elements from one of theillustrated embodiments in another of those embodiments. It will beunderstood, furthermore, that many other modifications and alternativesare possible within the scope of the invention.

I claim:
 1. A fluid-pressure operated pump comprising a pumping chamberhaving inlet and outlet openings for a fluid to be pumped and a fluidpressure driving chamber, a flexible diaphragm between the pumping anddriving chambers being displaceable by the fluid pressure in saiddriving chamber to pump fluid through the pumping chamber, said drivingchamber having an inlet for a supply of pressure fluid thereto and anoutlet valve comprising a valve member biased to close said valve, meansconnecting the outlet valve member to the diaphragm and permitting alimiting deflection of the diaphragm by the pressure of the fluid in thedriving chamber without displacement of the valve member from saidclosed position, diaphragm displacement by the pressure fluid beyondsaid limited deflection acting through said connecting means to displacesaid valve member to open the outlet valve and reduce the drivingchamber pressure, thereby reversing the direction of displacement of thediaphragm to permit the valve member to return to the valve-closingposition and allow the pressure in the driving chamber to increaseagain, said means connecting the outlet valve member to the diaphragmcomprising a connector member that is flexibly deformable for permittingrelative displacement between the valve member and the diaphragm withoutopening the outlet valve, said connection member comprising a unitary,one-piece unit with at least one of said diaphragm and said outletvalve.
 2. A pump according to claim 1 wherein said outlet valve member,flexibly deformable member and diaphragm are unitary, to form saidunitary, one-piece unit.
 3. A pump according to claim 1 wherein saidflexibly deformable member is a unitary elongate member extendingsubstantially centrally through the driving chamber.
 4. A pump accordingto claim 1 wherein said flexibly deformable member is unitary, and isresiliently biased to restrain opening of the valve when the valve is inthe closed position.
 5. A pump according to claim 1 wherein theconnection member is arranged to act as a collapsible strut to permitsaid limited deflection of the diaphragm relative to the outlet valve.6. A fluid-pressure operated pump comprising a pumping chamber havinginlet and outlet openings for a fluid to be pumped and a fluid pressuredriving chamber, a flexible diaphragm between the pumping and drivingchambers being displaceable by the fluid pressure in said drivingchamber to pump fluid through the pumping chamber, said driving chamberhaving an inlet for a supply of pressure fluid thereto and an outletvalve comprising a valve member biased to close said valve, a unitary,one-piece molding connecting the outlet valve member to the diaphragmand permitting a limited deflection of the diaphragm by the pressure ofthe fluid in the driving chamber without displacement of the valvemember from said closed position, diaphragm displacement by the pressurefluid beyond said limited deflection acting through said one-piecemolding to displace said valve member to open the outlet valve andreduce the driving chamber pressure, thereby reversing the direction ofdisplacement of the diaphragm to permit the valve member to return tothe valve-closing position and allow the pressure in the driving chamberto increase again, a unitary one-piece molding including at least one ofsaid outlet valve member and said diaphragm and providing said meansconnecting the outlet valve member to the diaphragm, the molding beingflexibly deformable for permitting relative displacement between thevalve member and the diaphragm without opening the outlet valve.
 7. Apump according to claim 6 wherein said molding comprises an elongatemember extending substantially centrally through the driving chamberbetween said valve member and said diaphragm, said member, said valvemember, and said diaphragm forming a one-piece unit.
 8. A pump accordingto claim 6 wherein said molding is resiliently biased to restrainopening of the valve when the valve is in the closed position.
 9. Afluid-pressure operated pump comprising a pumping chamber having inletand outlet openings for a fluid to be pumped and a fluid pressuredriving chamber, a flexible diaphragm between the pumping and drivingchambers being displaceable by the fluid pressure in said drivingchamber to pump fluid through the pumping chamber, said driving chamberhaving an inlet for a supply of pressure fluid thereto and an outletvalve comprising a valve member biased to close said valve, meansconnecting the outlet valve member to the diaphragm and permitting alimiting deflection of the diaphragm by the pressure of the fluid in thedriving chamber without displacement of the valve member from saidclosed position, diaphragm displacement by the pressure fluid beyondsaid limited deflection acting through said connecting means to displacesaid valve member to open the outlet valve and reduce the drivingchamber pressure, thereby reversing the direction of displacement of thediaphragm to permit the valve member to return to the valve-closingposition and allow the pressure in the driving chamber to increaseagain, said means connecting the outlet valve member to the diaphragmcomprising a strut-form connection member that is flexibly collapsiblefor permitting relative displacement between the valve member and thediaphragm without opening the outlet valve.
 10. A pump according toclaim 9 wherein the flexibly deformable member and the diaphragm areformed as an integral unit.
 11. A pump according to claim 9 whereinoutlet valve member and flexible deformable member are formed as anintegral unit.
 12. A pump according to claim 9 wherein said outlet valvemember, flexibly deformable member and diaphragm are formed as anintegral unit.
 13. A pump according to claim 9 wherein said flexiblydeformable member is an elongated member extending substantiallycentrally through the driving chamber.
 14. A pump according to claim 9wherein said flexibly deformable member is resiliently biased torestrain opening of the valve when the valve is in the closed position.